Lamp apparatus for improving wall darkening characteristics

ABSTRACT

Improved electric lamp apparatus exhibiting reduced bulb wall darkening includes a diffusion barrier immediately adjacent the interior of the lamp envelope wall in the general vicinity of the lamp electrode or electrodes. Diffusion barrier is a wire-like mesh or grid spaced only a small distance from the inner surface of the envelope and adjacent thereto. Barrier diameter is a very large fraction of envelope diameter so as to avoid affecting discharge current or constricting discharge. Diffused specie emanating from the electrode selectively deposits upon the diffusion barrier leaving the adjacent envelope wall clear.

1111 I 3,798,485 145-1 Mar. 19, 1974 22] Filed:

[ 1 LAMP APPARATUS FOR IMPROVING WALL DARKENING CHARACTERISTICS [75'] Inventor: Harald L. Witting, Saratoga, NY.

[73] Assignee: General Electric Company,

' Schenectady, NY.

' Sept. 29, 1972 21 Appl. No.: 293,326

[521' US. Cl...' 313/205, 313/217. 313/313.

' 313/348, 313/356 [51] Int. Cl..' H01k l/26, HOlj 1/52, HOlj 5/02 [58] Field ofrsearch 313/205, 195, 109, 204,

[56] T References Cited UNITED STATES PATENTS 2.232.816 2/194'1 Van 1 -1drn.'.... 313/114 x 2.300.997 11/1942 .Van Horn. t 313/348 X 2.812.465 11/1957 Germeshausm. (313/217 X :Que sseque 313/42 2/1961 Wiley 313/42 11/1950 Peters .1 313/195 Primary Examiner-James W. Lawrence Assistant Examiner-Marvin Nussbaum Attorney, Agent. or Firm-Jerome C. Squillaro; Joseph T. Cohen; Julius'J. Zaskalicky 57] ABSTRACT Improved electric lamp apparatus exhibiting reduced bulb wall darkening includes a diffusion barrier immediately adjacent the interior of the lamp envelope wall in the general vicinity of the lamp electrode or electrodes. Diffusion barrier is a .wire-like mesh or grid spaced only a small distance from the inner surface of the envelope and adjacent thereto. Barrier diameter is a very large fraction of envelope diameter so as to avoid affecting discharge .current or constricting discharge. Diffused specie emanating from the electrode selectively deposits upon the diffusion barrier leaving 1 theadjacent envelope wall clear.

' 7 Claims, 3 Drawing Figures PAIENTEDHAR 19 I214 3798x185 SHEET 1 BF 2 [F mi EOEEQ 2 53 2069524 was 4 2 4 5 6 GRID HEIGHT, H

PAIENIEDHAR 1 9 1914 3798' 485 sum 2 0F 2 LAMP APPARATUS FOR IMPROVING WALL DARKENING CHARACTERISTICS The present invention relates to electric lamp apparatus having improved diffusion barriers for the prevention of bulb wall darkening. More particularly, the invention relates to such devices in which the diffusion barrier is associated with the inner surface of the lamp envelope wall, rather than with the electrode which is the source of the wall darkening specie. This application is related to my own application Ser. No. 76,813, filed Sept. 30, 1970, now US. Pat. No. 3,683,226.

In the operation of electric discharge devices, such as electric lamps, the filaments or cathode electrodes thereof are usually raised to elevated temperatures, ei-

ther to cause direct incandescent radiation therefrom, to sustain a light emitting or stimulating electric discharge, or to emit electrons thermionically. In all cases, the specie of which the electrode so heated is fabricated is caused to dissipate by one or more of several mechanisms, including evaporation, sputtering, and sublimation. Material so removed from the heated electrode or electrodes is generally deposited upon the inner surface of the envelope wall.

Deposition of electrodematerial upon the envelope wall has several detrimental effects. In lamps, darkening of the bulb wall reduces the transparency of the envelope and decreases light output therethrough. The deposited specie absorbs radiation and becomes heated, raising the temperature of the lamp and accelerating the deterioration of the electrodes. Additionally, films formed by deposition of metallic specie upon the interior of the bulb wall are usually conducting and -causeleakage currents along the surface of the envelope wall, thus decreasing lamp efficiency and further increasing lamp operating temperature.

In the prior art, much work has been done to minimize the diffusion of such specie from the electrodes to the bulb wall. Other than gaseous transport cycles such as the iodide transport cycle, most such work has been concentrated 'on the problem of retaining electrode material at the electrodes, and has resulted in various means such as floating shields and the like, surrounding or closely adjacent the electrodes. To some extent, the foregoing efforts have increased electrode life, have retarded diffusion to the walls and slowed down the wall darkening process. These efforts have not, however, been completely effective to prevent wall darkening of the lamp envelope walls. Attempts to completely inhibit wall darkening by interposing mechanical shields in the vicinity of the cathode, have a point of diminishing return beyond which the detriment incurred outweighs the benefit. Thus, for example, undue emphasis on such structures, as for example that shown by Peters US. Pat. No. 2,530,990, tends to cause ion trapping and, in discharge'lamps, interferes with the lamp discharge, increases the potential drop at the cathode electrode and in general reduces electrode life. Such shields are characterized by close proximity to the .cathode. In the aforementioned Peters patent, the diameter of the shield is only one-half that of the envelope wall. Such shields also block some light output directly. Additionally, they tend to attract cathode material and stimulate the emission thereof by the cathode or filament due to electrostatic attraction because of close proximity thereto.

Accordingly, it is an object of the present invention to reduce bulb wall darkening of electric lamp apparatus by an interposed diffusion barrier without disadvantageously affecting the electrode efficiency or life.

Still another object of the present invention is to provide electric lamp apparatus having reduced bulb wall darkening, provided by a diffusion barrier which is spaced from the bulb wall.

Yet another object of the present invention is to provide electric lamp apparatus in which wall darkening is minimized by such a diffusion barrier without affecting electrical performance or reducing light output.

Briefly stated, in accord with the one embodiment of the present invention, I provide electric lamp apparatus including a heated electrode in an hermetically sealed light transmissive envelope. A partial pressure of at least a few torr of a buffer gas, such as argon, is provided therein. A diffusion barrier, in the form of a wirelike grid or mesh spaced from, but disposed immediately adjacent the inner surface of the bulb wall envelope, is located at the bulb wall. Vapors and particles of specie removed from the heated electrode preferentially deposit on the diffusion barrier, leaving the envelope wall relatively clear.

The novel features believed characteristic of the present invention are set forth in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by reference to the foregoing detailed description taken in connection with the appended drawing in which:

FIG. 1 is a schematic vertical cross-sectional view of a fluorescent lamp envelope embodying the invention;

FIG. 2 is a graphical plot illustrating the diffusion masking abilities of a diffusion barrier in accord with the invention.

FIG. 3 is a vertical cross-section view of an incandescent lamp in accord with the present invention.

In FIG. 1, a vertical cross-sectional view of a fluorescent lamp with the center portion broken away, in order to illustrate two different end structures including different diffusion barriers in accord with the present invention, is illustrated at 10. Lamp 10 includes a light transmissive, hermetically sealed envelope 1 I having a pinch 12 at one end thereof with a pair of lamp terminal inleads 13 extending thereinto. Each of the inleads 13 is connected with a flat ribbon 14 which ribbons are enclosed within pinch 12 and are connected by spot welding, for example, to the respective ends of a fluorescent lamp type filament 15, the structure of which is conventional and well-known to those skilled in the art. Within the portion of the lamp envelope immediately interior of envelope 1 1, a diffusion barrier 16 comprising individual wire members 17 is juxtaposed so as to remotely surround laterally the filament electrode 15 and to shield the same from direct line-of-sight communication with the interior of the bulb envelope 7 several times the average diameter of members 17 and, for optimum performance of the diffusion barrier, the inter-member spacing should be within the range of approximately 4 to times the average diameter of member 17. Since, as a practical matter, the diameter of the wires varies with the pressure within the bulb, wire diameter is within range of approximately 1 to 10 mils. This means that the diameter of the wire mesh is within the range of 98 percent to 80 percent of the interior diameter of envelope ll.

Diffusion barrier 16 may be a plurality of single lateral members or a single spiral-like wire member or, in the alternative, may be a properly dimensioned, in accord with the foregoing criteria, wire mesh which is similarly juxtaposed a similar predetermined distance from, but adjacent to, the interior of the bulb envelope wall. In the portion of lamp 10 illustrated in the righthand portion of FIG. 1, a crossed grid or mesh diffusion barrier lamp structure includes filament 21 which is laterally surrounded by diffusion barrier 22 which comprises transverse members 23 and longitudinal members 24 comprising a mesh as described hereinbefore.

The material of which the grid is fabricated is not particularly critical. Since no electric potential is required to be placed thereupon, the grid or mesh members may be conducting or nonconducting, although, in general, fabrication technology generally favors the use of malleable metallic members. It is naturally required that the material from which the diffusion barrier is constructed should be inert in the presence of any substance constituting the discharge medium. Thus, for example, if a mercury arc is a source of light or of excitation in the lamp environment, the material from which the diffusion barrier is fabricated should not react at the temperature and other characteristic parameters of the discharge with the mercury vapor. Similarly, if a sodium vapor discharge is utilized for light emission or stimulation within the envelope, the diffusion barrier should not be reactive therewith.

An atmosphere of a few torr, or higher, of a buffer gas such as argon or other inert gas is also included. If a mercury discharge lamp or a mercury-metallic vapor lamp or sodium vapor lamp embodies the invention, the envelope also includes a charge of the discharge sustaining and/or light emitting medium. If mercury is present for this purpose, it also serves as the buffer gas, if desired.

FIG. 2 comprises curves illustrating the improvement attained in tests of grid type embodiment of the invention, which tests record the transmission past the members of the diffusion barrier as a function at the distance, herein denominated as the height," of the barrier from the bulb wall and of the inter-member spacing within the diffusion barrier structure, herein denominated as grid spacing." Curves for grid spacing equivalent to 4, 6, 8, and 10 times the average diameter of the members comprising the structure of the diffusion barrier are plotted as a function of the grid height. As may be seen from the curves, which are exponential, a rapid drop occurs from an extrapolated zero height to a height of approximately two times member dimension, at which transmission past the grid has fallen to the value of less than 50 percent for the widest spacing and less than percent for a spacing of four times the average member dimension. From the curve of FIG. 2, it may also readily be seen that, with the barrier a distance of approximately 10 inter-member spacings from the envelope wall, the values of the transmission have fallen to less than 20 percent for all spacing values and less than 4 percent for spacing of four times the dimension. Further height increases tend to make the structure rather fragile, due to the support structure required.

From a consideration of the curves of FIG. 2, it is readily apparent that the present invention results in a very substantial diminution of the amount of specie evolved from a heated electrode in an electric lamp apparatus which is permitted to deposit upon the lamp envelope wall. It has been found, as illustrated in the curve of FIG. 2, that the degree of diminution of deposited specie upon the bulb wall is greatly disproportional to the actual physical masking caused by the diffusion barrier, in that only a fraction of the area to be masked need be obstructed with the members of the diffusion barriers in order to diminish by an extent of in excess of 50 percent and readily in excess of,75 percent of the amount which would ordinarily pass in the absence of the barrier. Thus, in accord with the present invention, it is possible to interpose a barrier adjacent the electrode in electric lamp devices which in of itself does not appreciably detract from the light transmissive character of the lamp envelope, while simultaneously greatly diminishing the amount of metallic specie from the lamp electrodes which is permitted to deposit upon the lamp envelope wall to cause the darkening thereof.

It is well known that shielded cathodes of the type shown by Peters U.S. Pat. No. 2,530,990 contain mesh shields which surround cathode structures and have as one function the dimunition of bulb wall deposition. Such shields, however, are primarily based upon a mechanism of constricting the discharge flow at the cathode, and increasing the current density J at the cathode. Such increased current density increases cathode temperature and results in greater emission of sputtered specie. The electrostatic potential of such shields tends to attract sputtered specie, which pass therethrough and darken the bulb wall.

In accord with the present invention, however, the diffusion barrier is removed from the discharge and the cathode so that in a 2 inch diameter incandescent lamp, for example, the mean diameter of the diffusion barrier, if made of 0.001 inch wire, is 1.98 inches, and if constructed of 0.010 inch wire is approximately 1.80 inches, both for a pressure of one atmosphere. Such barriers neither interfere with or constrict the discharge path nor increase sputtering from the cathode, but do collect sputtered and otherwise emitted specie preferentially, to reduce bulb wall darkening. The diameter of the individual wires comprising the barrier have an average value that is large as compared with the mean freepath of a molecule of the buffer gas. Thus, at 2 Torr the mean freepath is approximately 0.004 inch and decreases with increasing gas pressure.

The advantages of the diffusion barriers in accord with the present invention may be achieved with a variety of lamp structures. Thus, for example, FIG. 1 illustates a fluorescent lamp embodying the invention. In FIG. 3 of the drawing, an incandescent lamp, identified generally as 30, embodying the invention, includes a light transmissive envelope 31 and a screw base 32 having respective contact members 33 and 34. A glass pinch 35 supports filament support members 36, be-

vicinity of the-filament. The invention may similarly be utilized in the construction of high pressure mercury vapor lamps or of other type metallic vapor lamps such as disclosed and claimed in Reiling US. Pat. No. 3,324,421, and in Schmidt US. Pat. No. 3,026,210.

In all such lamps, the same general criteria are'followed and it is found that the closeness of the'spacing of the individual members of a diffusion barrier and the degree of penetration of the barrier into the volume of the envelope, as compared with the ratio of those dimensions to the average thickness dimension of the individual members comprising the barrier is a measure of the effectiveness of the barrier in diminishing the transmission of vapor particles to the bulb wall.

While the invention has been set forth herein with respect to certain examples and embodiments thereof, many modifications and changes will readily occur to those skilled in the art. Accordingly, I intend by the appended claims to cover all such modifications and changes as fall within the true spirit and scope of the present invention.

What I claim as new and desire to secure by letters Patent of the United States is:

1. Electric lamp apparatus comprising: a. an evacuable hermetically sealed light transmissive envelope; v b. an electrode member extending into said envelope and adapted to be heated to an operating temperature at which a constituent thereof is evolved and enters the volume of said envelope; I c. a partial pressure of at least a few Torr of a gas within said envelope; and d. a diffusion barrier comprising wire members juxtabuffer diffusion '6 posed immediately interior of the inner surface of said envelope and uniformly spaced therefrom laterally surrounding said electrode member to collect said evolved constituent and prevent deposition thereof upon saidenvelope wall without constricting any electric discharge within said envelopet 2. The apparatus of claim 1 wherein said diffusion barrier comprises a plurality of wire-like members vformed into a generally cylindrical grid and spaced apart from said envelope wall by a predetermined small distance and having a substantially uniform diameter within the range of approximately 80 to 98 percent of the interior diameter of saidenvelope wall.

. juxtaposed adjacent said envelope wall.

5. The apparatus of claim 2 wherein said wire-like I members arespaced apart form one another by a distance that is approximately 4 to 10 times the average diameter of said members.

6. The apparatus of claim 2 wherein said wire-like members are spaced from the inner surface of said envelope wall by a distance which is approximately 2 to 10 times the average diameter of said members.

7. The apparatus of claim 5 wherein said wire-like members are spaced from the inner surface of said envelope wall by a distance which is approximately between2 and 10 times the average diameter of said members. 

1. Electric lamp apparatus comprising: a. an evacuable hermetically sealed light transmissive envelope; b. an electrode member extending into said envelope and adapted to be heated to an operating temperature at which a constituent thereof is evolved and enters the volume of said envelope; c. a partial pressure of at least a few Torr of a buffer gas within said envelope; and d. a diffusion barrier comprising wire members juxtaposed immediately interior of the inner surface of said envelope and uniformly spaced therefrom laterally surrounding said electrode member to collect said evolved constituent and prevent deposition thereof upon said envelope wall without constricting any electric discharge within said envelope.
 2. The apparatus of claim 1 wherein said diffusion barrier comprises a plurality of wire-like members formed into a generally cylindrical grid and spaced apart from said envelope wall by a predetermined small distance and having a substantially uniform diameter within the range of approximately 80 to 98 percent of the interior diameter of said envelope wall.
 3. The apparatus of claim 2 wherein said grid comprises a coil of wire wound around the inner surface of said envelope wall, the diameter of said wire being large as compared with the mean freepath of a molecule of said gas.
 4. The apparatus of claim 2 wherein said grid comprises a mesh of substantially parallel crossed members juxtaposed adjacent said envelope wall.
 5. The apparatus of claim 2 wherein said wire-like members are spaced apart form one another by a distance that is approximately 4 to 10 times the average diameter of said members.
 6. The apparatus of claim 2 wherein said wire-like members are spaced from the inner surface of said envelope wall by a distance which is approximately 2 to 10 times the average diameter of said members.
 7. The apparatus of claim 5 wherein said wire-like members are spaced from the inner surface of said envelope wall by a distance which is approximately between 2 and 10 times the average diameter of said members. 